1. Field of the Invention
This invention belongs to the field of synthetic organic chemistry, and provides a process for selectively sulfonating one of the two unsubstituted amino groups on a 4-acyl-o-phenylenediamine. The products of the invention are intermediates in the preparation of antiviral benzimidazoles; some of them are new to chemistry.
2. State of the Art
Paget et al., U.S. Pat. No. 4,118,742, teaches the 1-sulfonylbenzimidazoles which are the ultimate products of the present process. The patent teaches a number of variations in the process used to prepare its compounds. In general, it first forms the benzimidazole with the 1-position unsubstituted, and then sulfonates it.
The patent explains (column 5 of the specification) that the sulfonation of the benzimidazole produces a mixture of isomers, which must ordinarily be separated. The problem arises from the fact that the desired antiviral benzimidazoles have a single substituent on the phenyl ring, usually preferably at the 6-position. The molecule is therefore asymmetric. Sulfonation of the benzimidazole by ordinary techniques is equally likely to sulfonate either of the nitrogen atoms, resulting in a mixture of isomers.
The advantage of the present invention, compared to the prior art processes, is that its ability to sulfonate selectively one of the amino groups of the phenylenediamine provides, after ring-closure, an excellent yield of the desired isomeric benzimidazole.
Some of the products of the present invention are taught and claimed by S. J. Dominianni in an application entitled Process of Preparing Chemical Intermediates, filed on the same day as the present application Ser. No. 373,945, now U.S. Pat. No. 4,483,986. Dominianni's process is only functional to make benzoyl compounds, where R is a phenyl group.